The present invention relates generally to residual stress and distortion induced in aluminum alloys, including aluminum alloy castings, during a quenching/cooling process. More particularly, the invention relates to systems, methods, and articles of manufacture to predict residual stresses and distortion in quenched aluminum castings after solution treatment.
Residual stresses are defined generally as stresses that remain in a product/component/object after manufacture processing. The residual stresses may be present in engineered castings, thin films, surface coatings, composites, and multiphase materials. Residual stresses may originate from a variety of sources. For example, macroscopic residual stresses may arise from heat treatment, machining, secondary thermal and mechanical processing, and assembling procedures, whereas micro-structural residual stresses often result from thermal expansion/contraction mismatch between phases and constituents, or from phase transformations. Manufacture components, such as aluminum castings, generally comprise some determinable level of residual stresses.
Aluminum castings often are subjected to a T6/T7 heat treatment to increase their mechanical properties. T6/T7 heat treatment generally includes a solution treatment at a relatively high temperature, followed by a quick quench in a cold or cool quench media, such as water or forced air, then age hardened at an intermediate temperature. Significant residual stresses and distortion may arise in aluminum castings, particularly those having complex geometric structures, due to what is typically a high non-uniformity of temperature distribution in the aluminum castings during quenching processes and particularly during rapid quenching, for instance in water. The presence of residual stresses and/or distortion in a structural component, such as an aluminum casting, can significantly and negatively influence the component's dimensional tolerance and performance. With increasing demand to reduce weight and improve fuel efficiency of automobiles, aluminum castings are being more widely used for critical automotive components, such as engine blocks, cylinder heads, and suspension parts. Such aluminum castings are often subjected to cyclic loading. Fatigue performance of aluminum castings may be significantly and negatively affected by the presence of residual stresses and, in particular, by tensile residual stresses in surface layers around the fillets area of the aluminum castings.
There are many ways to measure residual stresses in manufactured components, including those configured of aluminum alloys. Mechanical techniques such as hole drilling, curvature measurements, and crack compliance methods measure residual stresses in components based on respective component distortion. Diffraction techniques, such as electron, X-ray, and neutron, measure elastic strains in components due to residual stresses. Other techniques, including magnetic, ultrasonic, piezospectroscopy, photoelasticity, and thermoelastic, also are being developed. Mechanical techniques, however, generally are destructive of the component, while the accuracy of diffraction and other non-destructive techniques in measuring residual stresses generally depends on the extent of microstructure variation and geometric complexity of the component structure. In addition, it is generally impracticable to measure residual stresses in every location of a component not only because of the geometric constrains, but also because of the required time and cost to do so. As such, based on the foregoing, there exists a need for systems, methods, and articles of manufacture to accurately and computationally predict residual stresses and/or distortion of quenched aluminum castings.